Multiply tubing



May 13, 1941 c. A. NlcHoLs ET AL A 2,241,644

MULmIPLY TUBING Original Filed Aug. 5,' 1938 Patented May 13, 19412,241,644. MULTlrLY TUBING Charles A. Nichols and Raymond H. Bish,Anderson, Ind., assignors to General Motors Corporation, Detroit, Mich.,a corporation of Delaware Original application August 5, 1938, SerialNo.

223,245. Divided and this application September 9, 1939, Serial No.294,112

(Cl. 13S-62) 3Claims.

interstices between the seams and plies to bondthe seams and pliestogether.

This application is a division of Serial No. 223,245, filed August 5,1938, Patent No. 2,195,751.

It is a primary aim and object of the present --invention to provide anovel tube forming method and apparatus by which the formation ofmultiply tubing may be carried on continuously land at a relativelygreat speed of travel of the tube stock. 'Ihis object is accomplished byforming overlapping strips of steelI stock into multiply tubular shapeapproximately the shape of the finished product and then by swaging theapproximately formed plies of tubing into the desired shape with theplies substantially cylindrical and concentric and closely compactedtogether with their seams substantiallyplosed. More specifically theoverlapping portions of the strips are simultaneously formed intosemicyllndrical or half tubular portions of the conpleted plies. Thenthe outer ply is formed into approximately cylindrical formation andthen the inner ply is formed around a portion of the outer ply and intoapproximately cylindrical formation. Then follows the swaging operationwhich causes the plies to be compacted closely with the seamspractically closed. 'I'he resulting tubing comprises an inner layerprovided by lapping sections of the two plies of stock, and

l an outer layer likewise provided by lapping sections of the same twoplies of stock. In other words, each ply provides one half of the innerlayer and one half of the outer layer of the tubing. The advantages ofthis construction will be made apparent hereinafter.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawing, wherein a preferred embodiment of the present invention isclearly shown.

In the drawing:

The eleven figures of the drawing are sectional views showing varioussteps in the process of manufacturing tubing according to the presentinvention, Fig. l1 being drawn to a larger scale than Figs. 1 to l0.

The multiply tubing, lettered T in Fig. 1l, comprises an inner ply P1and an outer ply P2 having their edges beveled or scarfed at 20 angles.

'For 1/4" O. D. tubing the plies of steel are .013"

to .015 thick. Before scarring, the plies are .7275" to .7325" wide andare scarfed to .743" to .748" wide. The plies are scarfed by means ofscarfing rollers designed to produce the required bevel. The ply stripsP1 and P2 are unwound from supply reels by the operation of the tubefonning apparatus, all of which is disclosed in Patent No. 2,195,751.The plies pass first through a degreaser which removes all of the oilpreviously placed upon the strip steel to protect it from rust. Y

The cleansed plies P1 and P2 then Pass to an oiler which applies oil tothe inner surface of the inner ply P1 and to the outer surface of theouter plyV Pz but not to adjacent surfaces of the two plies. Lubricationof the plies is necessary in order to reduce friction and prevent thegalling of the arbor or mandrel and rolls of the forming apparatus bythe plies of steel passing through. A close control of the amount of oilon the plies is imperative. To control the amount of oil, the plies arerst passed through the degreaser to remove all of the oil previously onthe plies and a wick type oiler is used to apply the correct amount ofoil of known composition. Any light oil free of sulphur, such ascommercial ceresinol, would -be satisfactory. The amount of oil suppliedis suilicient for the lubrication of material as it passes through theforming apparatus and a slight amount of oil will remain lon the insideof the tubing as it enters the brazing furnace. This oilforms a gas inthe brazing furnace which combines with the oxygen inside the tubing andprevents oxidation of the inside of the tubing. The exterior of thetubing is protected while passing through the brazing furnace byintroducing into the furnace a supply of reducing gas. The adjacentsurfaces of the plies P1 and P2 should be free from oil, since no usefulpurpose is served by applying oil to these surfaces. The amount of oiltaken by the tubing into the brazing furnace should be as small aspossible in order to eliminatethe carburizing effect of this oil.Therefore, the oiler is constructed so as no t to place any oil betweenthe plies.

The plies P1 and P2 are progressively shaped as indicated by Figs. 1 to11 by passing the plies between sets of forming rolls which are gearedtogether and to va. source of power so that the peripheral speed ofsurfaces of the rollers' engaging the plies is substantially the same.

For the manufacture of 1;/4" O. `D. tubing, a speed of 18 ft. per min.has been found satisfactory. All of the guides and rolls are made ofchromium plated hardened steel.

The plies P1 and Pz pass through a device which determines the amount ofoverlap of the plies. Then the plies pass between a first set.

of rolls which form a curve on the outside edge of each ply, asindicated by e1 'and en. While the plies pass from the first set offorming rolls to the second set, they are guided by a channel.

The turned-up edges e1 and e2 of the plies co.

the way in from the edges of the overlapping,

parts of the plies. 'Ihe work thus formed passes through another guidebefore entering between the third set of rolls.

A third set of rolls forms the work into the shape indicated in Fig. 3.The non-overlapping parts extend roughly at an angle of 60 and theoverlapping parts are formed somewhat into cylindrical formation. f

Then the work passes through a suitable guide from the third set to-thefourth set of rolls where the work is formed as shown in Fig. 4 whereinthe non-overlapping parts of the plies are roughly parallel. Between thefourth and fifth set of rolls the plies move into cooperative relationwith a mandrel which is supported by means which extends down betweenthe plies when in the position shown in Fig.. 4.

Up to the point where the stock enters between the lfifth set of rolls,the rolls and guides previously referred to have caused the work to beshaped so that the overlapping portions of the plies have been formedsimultaneously into approximately one-half cylindrical portions. Betweenthe fifth set of rolls the completion of the formation of the outer plyP2 is begun. This fifth set of' rolls changes the shape from that shownin Fig. 4 to that shown in Fig, 5. By means of the sixth and seventhsets of rolls the ply Pz is shaped as shown in Figs. 6 and '7. Then thework passes through an eighth set of rolls which cause the ply Pz to beformed in close proximity to the mandrel and which begins the formationof the non-overlapping portion of the ply P1.

The work then passes through the 9th and 10th sets of rolls which formthe ply P1 as shown by Figs. 9 and 10, respectively. Fig. 10 shows thatthe plies have been formed only approximately into cylindrical formationand that the plies have not been compacted together so that the spacebetween them is at the minimum and so that the edges of the inner pliesare abutting and the beveled edges of the outer plies arecompletelyoverlapping. The completion of the formation of the tubing T withclosely compacted plies and closely contracted seams as shown in Fig. 11on an enlarged scale, is effected by a rotary swaging machine disclosedin my Patent No. 2,195,751. As the tubing moves longitudinally over themandrel, the rotary swager causes the plies, loosely formed as shown inFig. 10, to be tightly compacted as shown in Fig. 11.

The tubing then passes into the brazing furnace in which the temperatureof the tubing is,

elevated to about 2100 F., and in which the tubing passes through a bathof copper which,

lby capillaryattraction, almost instantly enters and fills theinterstices between the seams and plies of the tubing. yTheexcess'copper is wiped -layer of tubing comprises a, portion of theinner ply and a portion of the outer ply. Since the plies areinterlocking, there can be no angular i displacement of one ply withrespect to the other. Where multiply tubing is formed from separateplies of stock in a manner such that the inner layer of the tube isprovided inl its entirety by one ply and the outer layer in its entiretyby another ply, it is possible for an angular displacement between thetwo plies to take place during the formation of the ftubing. Thisdisplacement is known as spiraling and occurs more frequently in largersizes of tubing where the outside strip has a tendency to spiralindependently of the inside strip. Therefore, the result is that, incertain places along the length of the tube, the seams may beadjacent.This is objectionable because the tube is not as strong where the seamsare adjacent. Since .the forming rolls shape the plies for interlockingengagement, the swager must necessarily'form diametrically opposite jogsin the plies which give the interlocking effect. Therefore, if the tubespiralsI at all while being formed, it must spiral as a whole. Since,due to the interlocking of the strips, they cooperate together to resistspiraling, there is twice the tendency to prevent a spiral.

Another advantage of the present method of forming tubing is thattighter seams are formed than in the case where an attempt is made tobutt the bevelled edges of the same ply to form the seam. The scarfed orbeveled edges of the plies naturally tend to lie compactly along thejogs or offsets, hence there is no appreciable tendency to form voids inthe seams near the scarfed edges.

A further advantage is that there are two seams appearing on theexterior of the tube; therefore, it is always easy to tell that, theseseams are properly spaced apart. Furthermore, the two seams provide twopaths for the entrance of copper between the plies.

Still another advantage is that both plies are of the same width. Thisfeature requires that there be only one-half the number of differentsizes of stock as would be required for the manufacture of tubing inwhich the inner layer of tubing is4 provided entirely by the inner plyand the outer layer of the tube entirely by the outer ply. Naturally,only one-half the number of manipulations are required to yset up ascariing machine for a particular size of tubing.

While the embodiment of the present invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be "adopted, all coming Within the s'cope of the claims plyclosely fitting against the jog portion of the strip stock, each of theplies forming a portion of the inner wall of the tube and a portion ofthe outer Wall of the tube, each ply having its outer Wall portioncompletely covering the inner Wall portion of the other ply.

2. A double-wall tube comprising tWo plies of strip stock, each of theplies having a cylindrical portion forming a part of theA inner wall ofthe tube and having a cylindrical portion forming a part of the outerWall of the tube, said portions merging with a. jog portion whichextends from the inner Wall to the outer wall, the edges of one CHARLESA. NICHOLS. RAYMOND H. BISH.

